CN111788057B

CN111788057B - Method for producing press-molded article

Info

Publication number: CN111788057B
Application number: CN201980016101.9A
Authority: CN
Inventors: 武部佳树; 筱原光太郎; 本间雅登
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2018-03-30
Filing date: 2019-03-25
Publication date: 2022-05-31
Anticipated expiration: 2039-03-25
Also published as: WO2019188873A1; EP3778173B1; TW201941915A; CN111788057A; EP3778173A1; TWI791803B; EP3778173A4; US20210154952A1; JPWO2019188873A1; JP7163911B2; KR20200135938A

Abstract

The invention provides a molded article which realizes low specific gravity and high rigidity at the same time and inhibits wrinkles and scratches and a manufacturing method thereof. A method for producing a press-molded article, comprising press-molding a sheet-like molding base material, which is disposed in a cavity of a molding die and in which reinforcing fibers are randomly dispersed in a matrix resin, using a press-molding machine having a molding die and a molding die, wherein the molding die has a convex portion and a concave portion, the convex portion corresponds to the concave portion, the cavity is formed between the concave portion and the convex portion, and the molding die has at least one surface (B) that is a surface (A) orthogonal to a direction of pressure applied from the press-molding machine to the molding die and that is a surface in which the applied pressure is in a range of 0 to 70% with respect to the surface (A) when the pressure applied from the press-molding machine to the surface (A) is 100%, the manufacturing method comprises the following steps: a shaping step (III) for applying a surface pressure of 1MPa or more to the surface (A) or the molding base material as an external pressure from the press molding machine; and a pressure maintaining step (IV) for adjusting the pressure applied to the molding base material from the press molding machine as an external pressure to 0.1MPa or less after the shaping step (III).

Description

Method for producing press-molded article

Technical Field

The present invention relates to a method for producing a press-molded article containing at least a reinforcing fiber and a matrix resin.

Background

In recent years, demands for increased rigidity in the market have been increasing year by year for industrial products such as automobiles, aircrafts, sporting goods, and electronic devices. In order to meet such a demand, products using a sheet-like molded substrate containing a fiber-reinforced resin having excellent rigidity are widely used in various industrial applications. Among them, for the purpose of obtaining a reinforcing effect by the shape of a product, a press molding method for obtaining a molded article having not only a planar shape but also a standing wall portion, and techniques related to improvement of formability of a sheet-shaped molded base material by a heating technique have been proposed (see patent documents 1 to 3).

For example, in a method of performing press molding for improving the shaping property in an investigation of a laminated structure of a sheet-like fiber-reinforced resin for forming a standing wall shape in a press-molded product (see patent document 1), an investigation of an optimum melting temperature when a thermoplastic resin in the fiber-reinforced resin is melted is known (see patent document 2). As a molding technique for deep drawing a shape, which is generally considered to be difficult, a molding method has been studied in which a fiber-reinforced resin is pressed into a molding die and broken when the shape is shaped by disposing a film on the surface of the fiber-reinforced resin (see patent document 3).

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5332227 Specification

Patent document 2: japanese patent No. 5459005 Specification

Patent document 3: japanese laid-open patent publication No. 6-344431

Disclosure of Invention

Problems to be solved by the invention

However, in a method of molding a sheet-like molding base material containing a fiber-reinforced resin, particularly a press molding method in which productivity is also taken into consideration, it is necessary to obtain a molded article free from appearance defects with high accuracy. However, when the molded article has a shape such as a standing wall, it is difficult to keep the pressure applied from the press-molding machine to the sheet-like molding base material constant due to the restriction of the shape of the article. Therefore, no research has been conducted for applying the same pressing pressure to a sheet-like shaped substrate.

In addition, in order to accurately obtain the dimensions and surface appearance of a molded article obtained by press-molding a sheet-like molding base material at the time of press molding, it is necessary to adopt the following production method: the sheet-shaped molding base material is shaped by gradually deforming it by providing a secondary material such as a film, providing a special mechanism on the molding die, or performing a plurality of molding processes. Therefore, productivity and economy are deteriorated due to preparation of subsidiary materials, increase in the number of press molding processes, introduction of dedicated equipment, and the like. Further, since the pressure applied to the sheet-like molding base material by the press molding machine becomes uneven due to the restriction of the product shape, a portion having a very low pressure and a portion having a very high pressure are mixed in the molding base material, and the molded product has poor appearance such as wrinkles and scratches and a decrease in mechanical properties.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing a press-molded product which can easily form a complicated shape such as a standing wall without providing any special subsidiary material or molding equipment and has an excellent surface appearance.

Means for solving the problems

A method for producing a press-molded article, wherein a sheet-like molding base material, which is disposed in a cavity of a molding die and in which reinforcing fibers are randomly dispersed in a matrix resin, is press-molded by using a press-molding machine provided with the molding die,

the molding die comprises a molding die for a convex portion and a molding die for a concave portion for forming an opening portion of a molded article, the molding die for the convex portion corresponds to the concave portion, a cavity is formed between the molding die for the concave portion and the molding die for the convex portion, and,

the molding die has at least one surface (B) which is a surface (A) orthogonal to the direction of pressure applied from the press molding machine to the molding die, the surface (B) having a pressure applied in the range of 0 to 70% with respect to the surface (A) when the pressure applied by the press molding machine to the surface (A) is set to 100%,

the manufacturing method comprises the following steps:

a shaping step (III) for applying a surface pressure of 1MPa or more to the surface (A) as an external pressure from the press molding machine; and

and a pressure holding step (IV) for setting the pressure applied from the press molding machine to the molding base material as an external pressure to 0.1MPa or less without releasing the molding die after the shaping step (III).

Effects of the invention

According to the present invention, it is possible to provide a method for producing a press-molded article having excellent formability and appearance quality even in a shape to which a sufficient pressure force cannot be applied from a press-molding machine.

Drawings

Fig. 1 is a schematic diagram showing an example of a positional relationship between a platen and a molding die of a press molding machine.

Fig. 2 is a schematic view showing a direction and a state in which a molding die is clamped by a pressing force applied from a press molding machine.

Fig. 3 is a schematic diagram showing an example of the relationship between the angles of the surface (a) and the surface (b) in the press plate and the molding die of the press molding machine.

FIG. 4 is a schematic view showing an example of a molded article.

Fig. 5 is a schematic view showing an example of a state of dispersion of reinforcing fibers in the reinforcing fiber mat used in the present invention. (a) Is a top view. (b) Is a thickness direction sectional view.

Detailed Description

The method for producing a press-molded article according to the present invention will be described below. First, the "pressure" and the "surface pressure" disclosed in the present invention will be described.

In the present invention, the "surface (a) orthogonal to the direction of pressure applied from the press molding machine to the molding die" means a horizontal virtual surface orthogonal to the direction of pressure applied from the outside to one surface of the platen attached to the molding die. The term "a" as used herein means that the surface (a) is parallel to one surface of the pressure plate to which pressure is applied. When the molding die is disposed in the press molding machine, the molding die is often a horizontal surface of the molding die.

The "pressure applied to the surface (a)" is equivalent to a pressure applied from the molding machine to one surface of the platen. Further, the pressure applied to the molding die is equal to the pressure applied to the same projected area in the direction of the pressure applied to the molding die. The expression "a surface (B) having an applied pressure in the range of 0 to 70% with respect to the surface (a) when the applied pressure is 100% with respect to the surface (a)" means an inclined surface in a mold for forming a concave portion of an opening of a molded article and a mold for forming a convex portion corresponding to the concave portion, and a tangent line at each portion of the inclined surface is substantially 45 ° to 90 ° with respect to a horizontal plane. The inclined surface includes a curved shape and a spherical shape in addition to a linear shape. This means that: when a pressure applied from a molding machine in a direction perpendicular to a platen is applied to an inclined surface having an angle, the pressure is decomposed into a force applied in the direction perpendicular to the inclined surface and a force applied in the direction of the inclined surface, and the force applied in the direction perpendicular to the inclined surface is 0-70%. Here, 0% means a case of being perpendicular (angle 90 °), and 70% means a case of being substantially 45 °.

In the present invention, the term "forming die having at least one surface" means that a forming die for forming a three-dimensional shape, such as a deep drawing die, includes a standing wall having at least one surface of substantially 45 ° to 90 °.

In the present invention, a molding die having a surface (B) is used, wherein the surface (B) is a surface having a surface pressure in the range of 0 to 70% relative to the surface (A) when the surface (A) horizontal to the surface orthogonal to the pressure direction applied from the press molding machine is taken as a reference and the pressure applied to the surface (A) is taken as 100%. It is also preferable to have the surface (a) in some cases, but the present invention is not limited thereto. The surface (a) is a surface horizontal to a surface orthogonal to the direction of pressure applied from the press molding machine, and is an imaginary surface and is not limited to a surface actually existing in the molding die. In a molding die formed by a die for forming a concave portion and a die for forming a convex portion of an opening portion of a molded article, a surface (A) is an imaginary plane which is horizontal to a plane orthogonal to the direction of a pressing force applied from the outside of the molding die by a pressing plate attached to the molding die. On the other hand, the molding die includes at least a surface (a) and a surface (b). Fig. 2 is a view showing a molding die and a pressure applying method. In fig. 2, the direction 7 of application of the pressing force from the press molding machine is the direction of the pressing force applied to the molding die, and is the same direction as the direction of gravity. The cavity 6 is a gap portion generated when the molding die is closed, and corresponds to the shape of the molded product. In this case, if the surface (a) of the molding die is horizontal with respect to the gravity direction, the horizontal surface (a) corresponds to the surface (a), and the molding die has the surface (a). On the other hand, if the surface (a) of the molding die is not horizontal with respect to the direction of gravity, the surface (a) does not belong to the surface (a), and the molding die does not have the surface (a).

The molding base material disposed in the cavity 6 of the molding die is shaped into the shape of the molding die to form a surface. In the molded article, there may be a surface corresponding to all or a part of a surface (a) horizontal to a surface orthogonal to the direction of pressure applied from the press molding machine (fig. 4, reference numeral 11).

Next, the following describes the above (B). The surface (B) is a surface to which a pressure applied to the surface (A) (virtual surface) is in the range of 0 to 70% of the pressure applied to the surface (A) by the press forming machine. The molding die has a surface (B), and at least one surface of the surface (B) corresponds to the surface (B). The surface (b) is a surface to which a pressure is applied in a range of 0 to 70% of the pressure applied to the surface (A) by the press molding machine, and there may be a plurality of surfaces. The molding base material disposed in the cavity 6 of the molding die is shaped into the shape of the molding die and formed on the surface (B) (fig. 4, reference numeral 12).

For the surface (B), "a tangent line at each part of the inclined surface" will be described. In the case where the inclined surface is linear (for example, a molding die shown in fig. 2), the inclination of the tangent line at each portion of the inclined surface is the same. On the other hand, when the inclination changes although the inclination is linear, the inclination of the tangent line differs at each portion. In addition, when the inclined surface is curved, the inclination of the tangent line may be different at each portion. The surface (B) is a surface in which the inclination of at least the tangent to the central portion of the molding die, among the tangents to the respective portions of the inclined surface, is substantially 45 DEG to 90 DEG with respect to the horizontal plane. Here, the tangent line at the center of the molding die means a tangent line at a position that is half of the height between the upper end and the lower end where the inclination starts when the inclined surface in the molding die is projected in the cross-sectional direction. Fig. 2 is a sectional view of the molding die, but when the molding die protrusion 4 is illustrated, it is a tangent line at a position of the center position (M) in the height direction of the upper end (U) of the inclined surface and the lower end (L) of the inclined surface.

In the shaping step and the pressure holding step, if the molding base material is brought into contact with the molding die, the pressure applied to the molding base material is equal to the pressure applied to the surface (a) and the surface (b) of the molding die.

In the present invention, "the surface pressure pa (mpa) applied to the surface (a) and the surface pressure pb (mpa) applied to the surface (b)" mean: the same pressure is applied in a direction perpendicular to the surface (a), that is, the same surface pressure as that applied to the molded substrate in contact with the surface (a); and the same pressure applied in the direction perpendicular to the surface (b), that is, the same surface pressure applied to the molded substrate in contact with the surface (b).

[ Forming die ]

The molding die used in the present invention will be described with reference to fig. 1. The molding die of the present invention has a die for forming a concave portion of an opening of a molded article and a convex portion corresponding to the concave portion, and a cavity is formed between the convex portion and the die for forming the concave portion. As shown in fig. 1, the molding dies are formed of a pair of male and female (3, 4) dies which are attached to at least a concave portion and a convex portion of upper and lower platens (1, 2) of a press molding machine. These molding dies have cavities corresponding to the shapes of the molded articles. The cavity (6) is a gap portion generated when the mold is closed as shown in fig. 2, and corresponds to the shape of the molded article.

The molding die of the present invention preferably has at least two surfaces, i.e., a surface (a) having an inclination of 0 to 60 degrees with respect to the surface (a) (an angle of 8 in fig. 3 is 0 degree, and a die of a concave portion is shown in fig. 3) and a surface (b) having an inclination of 45 to 90 degrees with respect to the surface (a) (an angle of 9 in fig. 3 is 60 degrees, and a die of a concave portion is shown in fig. 3), so that the product design can be widened. In this case, the case where the inclination of the surface (a) is 0 degree is the same as the case of the surface (a), and the surface (B) corresponds to the surface (B). Since the surface (a) has an inclination of 0 to 60 degrees with respect to the platen of the press molding machine, the pressing force from the press molding machine is sufficiently applied to the sheet-like molding base material in the shaping step (III) described later, and therefore the thickness of the press molded product is easily controlled, which is preferable from the above viewpoint. For the same reason, the inclination of the surface (a) with respect to the surface (a) is more preferably 0 to 45 degrees, and particularly preferably 0 to 15 degrees. At 0 degrees, the surface (a) is the same as the surface (a). Further, since the surface (b) has an inclination of 45 to 90 degrees with respect to the surface (a), it is possible to prevent an excessive pressure from the press molding machine from being applied to the sheet-like molding base material when the sheet-like molding base material is press-molded, and it is possible to prevent the sheet-like molding base material from excessively moving in the cavity of the molding die, and to improve the surface appearance of the molded article, which is preferable. For the same reason, it is more preferable that the inclination of the surface (b) is 60 to 90 degrees with respect to the surface (a). In the molding die used in the present invention, the corner portion between the surface (a) and the surface (b) may have an R-shape as appropriate depending on the product design, from the viewpoints of ease of shaping the sheet-like molding base material in the shaping step (III) and ease of cleaning the cavity of the molding die after the molded article is taken out.

[ Press Molding Process ]

The manufacturing method of the present invention is a method for press-molding a sheet-shaped molding base material including reinforcing fibers and a matrix resin, and uses a molding die having a surface (B) (12 in FIG. 4 (B)) in which at least a surface pressure applied to the molding base material in a molding die cavity is in a range of 0 to 70% with respect to a surface (A) (11 in FIG. 4 (a)) when a pressure applied to the surface (A) (11) with respect to a surface horizontal to a surface orthogonal to a pressure direction applied from the press-molding machine is set to 100%.

Examples of the surface (B) include a box-shaped standing wall portion, a portion of a quadrangular pyramid shape having a slope in the height direction other than the apex, and a portion of a hemisphere shape having a curvature in the height direction. When the pressure against the surface (B) is in the range of 0 to 70%, scratches, wrinkles, and the like, which are regarded as molding defects of the molded article, can be suppressed, and therefore the appearance quality of the molded article is improved. From the viewpoint of achieving a constant molding pressure, which is an effect of the present invention, the range of 0 to 50% is preferable. On the other hand, if the deviation is within the range of 0 to 70%, an excessive pressure is applied to the sheet-like molding base material disposed on the surface (B) of the molded article, and the movement (displacement) of the molding base material in the cavity of the mold is caused during press molding, and wrinkles are generated on the surface of the molded article, which is not preferable.

An example of a method for press-molding a sheet-like molding base material containing reinforcing fibers and a resin according to the present invention is as follows.

A step (I): a step of heating the molding base material of the molding base materials to melt the thermoplastic resin

Step (II): disposing the melted molding base material in the cavity of the molding die

Step (III): a shaping step of applying a surface pressure of 1MPa or more to the surface (A) from a press forming machine

Step (IV): a pressure maintaining step of applying a surface pressure of 0.1MPa or less to the shaped molding base material from the press molding machine while fixing the molding shape

Step (V): a step of taking out the molded article from the molding die after the surface temperature of the cavity of the molding die is lowered

Here, the step (III) of performing the shaping and the step (IV) of performing the pressure holding for fixing the shape of the shaped molding base material are essential components. The shaping step (III) is a step of shaping the sheet-like molding base material into the shape of the molded article, in other words, to make the sheet-like molding base material follow the shape of the molding die cavity 6. In this step, by applying an external surface pressure of 1MPa or more to the surface (a) from the press molding machine, a sufficient pressurizing force can be applied to the sheet-shaped molding base material, the thickness can be controlled, and the shape of the molded article can be stabilized. Generally, the time for applying pressure from the press forming machine is about several seconds. The external surface pressure of 1MPa or more applied from the press molding machine is confirmed by a pressure gauge attached to the molding machine. The pressure applied from the molding machine is applied to the molded base material via the face (a) and the face (b) of the molding die. The "opposing surface (a)" can be interpreted as "surface (a) of the molding die" when the molding die has a horizontal surface with respect to the platen. Preferably 3MPa or more, and more preferably 5MPa or more. If the surface pressure applied to the surface (a) is less than 1MPa, it is not preferable to apply a sufficient pressure to the reinforcing fibers or resin in the molding base material, and it is difficult to control the thickness of the molded product. The upper limit value of the surface pressure is not particularly limited, but is 20MPa from the viewpoint of preventing the reinforcing fibers in the molding base material from being broken by the pressure and preventing the mechanical properties of the press-molded article from being degraded. The pressure holding step (IV) is a step of applying a surface pressure of 0.1MPa or less to the molded base material. Here, the pressure holding step is a step of fixing the shape of the molding base material having the shape formed in the shaping step (III), and contributes to dimensional stability and appearance quality of the molded product.

The details of each step will be described below.

In the step (II) of disposing the molten molding base material in the cavity of the molding die, it is preferably disposed so as to cover 90% or more of a projection surface of the cavity in a direction orthogonal to the direction of pressure applied from the press molding machine. This is preferable from the viewpoint of suppressing the occurrence of a defect in the molded product, because the molding material can be filled up to the end of the obtained molded product.

In addition, from the viewpoint of adjusting the thickness of the molded article and the degree of freedom in design based on product design, it is preferable that the step (II) be performed by laminating 2 or more layers of the sheet-like molding base material. The number of layers to be stacked is not particularly limited, but is preferably selected according to the thickness of the product. In the case where the resin constituting the molding base material is a thermoplastic resin, a heating step may be performed to melt the thermoplastic resin in the cavity of the molding die during the press molding of the molding base material. Therefore, in order to improve the heating efficiency, it is preferable to arrange materials having a thickness of 1mm or less in parallel in the heating device, and form a stack immediately before the arrangement in the cavity of the molding die.

In the case where the molding base material is a laminated laminate, it is preferable that the surface temperature of the molding cavity is adjusted to a temperature equal to or higher than the curing temperature or the solidification temperature and equal to or lower than the decomposition temperature of the resin in the sheet-like molding base material in advance before the laminated molding base material is placed in the molding cavity, from the viewpoint of improving the surface appearance of the molded product and the production rate.

In the case where a thermosetting resin is used as the sheet-shaped molding base material, it is preferable to apply sufficient heat for melting or softening the thermosetting resin before forming the crosslinked structure and curing, from the viewpoints of easiness of thickness control and production speed of the molded article to be press-molded. The temperature at which the resin in the molding base material is cured can be determined by dsc (differential Scanning calibration). The temperature rise rate was 10 ℃/min, and the range of. + -. 20 ℃ from the temperature of the peak top of the exothermic peak in the obtained DSC curve was defined as the curing temperature.

In the case where the sheet-shaped molding base material is a thermoplastic resin, it is preferable to obtain sufficient heat for solid-stating the melted or softened sheet-shaped molding base material by heating from the viewpoint of thickness control and production speed of the produced press-molded article, and as a more preferable aspect, it is preferable to perform the temperature of the molding die cavity within a temperature range higher by 20 to 50 ℃ than the solid-stating temperature of the thermoplastic resin constituting the sheet-shaped molding base material from the viewpoint of easiness of shaping of the plasticized sheet-shaped molding base material and surface appearance of the molded article. For example, when a polyamide 6 resin is used as the resin, the temperature can be preferably in the range of 200 to 250 ℃, and when a polypropylene resin is used, the temperature can be preferably in the range of 180 to 210 ℃. The range may be obtained by combining any of the above upper limits with any of the above lower limits. The solid-state temperature of the resin in the molding base material can be determined by dsc (differential Scanning calibration). The measurement was performed at a temperature increase rate of 10 ℃/min, and the start point of the increase of the melting peak in the obtained DSC curve was defined as the solid-state temperature.

In view of obtaining a molded article having excellent surface properties, the upper limit of the surface temperature of the cavity of the molding die is preferably set to a temperature at which the resin component of the resin in the molding base does not reach thermal decomposition.

In the shaping step (III) in which a surface pressure of 1MPa or more is applied to the surface (A) by the press molding machine, the surface pressure Pa (MPa) applied to the surface (a) and the surface pressure Pb (MPa) applied to the surface (B, b) preferably satisfy 0.2 XPa Pb < 2 XPa. When a plurality of faces (B, b) are present, it is preferable that all the faces (B, b) satisfy the condition of 0.2 XPa Pb 2 Pa. In the surface (B), it is preferable that an excessive pressure is not continuously applied to the molding base material by the press molding machine, and appearance defects such as movement (displacement) of the molding base material in the cavity of the molding die and generation of wrinkles on the surface of the press molded product during press molding can be suppressed. For the same reason, it is more preferably in the range of 0.5 XPA. ltoreq.Pb. ltoreq.Pa. The range may be obtained by combining any of the above upper limits with any of the above lower limits.

In addition, in the shaping step (III), it is preferable that the surface pressure applied to the sheet-like molding base material on the surface (a) in the cavity after the mold is clamped is within a range of ± 10% of the average value of the pressure applied to the surface (a), since the occurrence of appearance defects such as wrinkles on the surface of the molded article can be suppressed. The smaller the variation, the more preferable, but a practical range of ± 5% or less can be exemplified. Similarly, when the surface pressure applied to the sheet-like molding base material on the surface (B, b) in the cavity after the mold is clamped is within a range of ± 10% of the average value of the pressures applied to the surfaces (B, b), appearance defects such as wrinkles on the surface of the molded article can be suppressed, which is preferable. The smaller the variation, the more preferable, but a practical range of ± 5% or less can be exemplified. The range may be obtained by combining any of the above upper limits with any of the above lower limits.

In the shaping by press molding, since the sheet-like molding base material is introduced into the cavity or folded to be shaped, a standing wall portion of the molded article and the like are easily formed, and the surface appearance of the obtained molded article is improved. The sheet-like molding base material preferably covers 100% or more of the projection surface of the molding die cavity.

In addition, from the viewpoint of ease of shaping the molded article, it is preferable to include a preforming step of previously processing the shape of the sheet-like molding base material into the developed shape of the molded article before the step (III). The developed shape is preferable because, in the shaping step (III), it is possible to prevent a sheet-like molding base material from being excessively present at a corner portion in the shape of a molded article represented by, for example, a box shape. In addition, in the case of a shape in which a developed shape is not established, such as a hemispherical shape or a rib shape having irregularities on a surface, it is not necessary to make all of the molded articles to be obtained planar, and an overlapping portion may be provided at an end portion.

Step (IV): a pressure maintaining step of applying a surface pressure of 0.1MPa or less to the shaped molding base material and fixing the molding base material in a molded shape

The manufacturing method according to the present invention includes a step of applying a surface pressure of 0.1MPa or less to the molded base material from the press molding machine as the holding pressure step (IV). Here, the pressure holding step is a step of fixing the shape of the molded substrate having the shape formed in the shaping step (III), and contributes to dimensional stability of the molded product. Further, the pressure holding step (IV) is performed without releasing the molding die after the shaping step (III). This provides excellent dimensional stability. By setting the external pressure from the press molding machine in the holding pressure step (IV) to 0.1MPa or less, dimensional change of the shaped sheet-like molding base material can be temporarily suppressed. This pressure is confirmed by a pressure gauge or the like attached to the molding machine. The surface pressure of 0.1MPa or less as used herein means a pressure applied by a press, and the pressure may be 0MPa, but since the mold is not released after the pressing to remove the pressure, the pressure is continuously applied to the shaped molding base material. If the external pressure from the press molding machine in the holding pressure step (IV) is more than 0.1MPa, the molding base material flows or deforms, and the shape stability deteriorates, which is not preferable. In the pressure holding using a press molding machine, in general, there can be exemplified: a method (pressure removal method) of isolating the supply of the pressurizing force from the press molding machine to the shaped sheet-like molding material by releasing the molding pressure; in the method of controlling the position of the platen of the press molding machine to set the sheet-like molding material to be shaped to a state where substantially no pressure is applied to the molding material, it is preferable that the pressure holding step (IV) is performed in a state where the platen of the press molding machine is maintained at the position where the shaping step is performed without being released from the press molding die from the viewpoint of controlling the thickness of the molded product to a desired thickness. The pressure control method is represented as a position control method.

The face pressure Pa (MPa) applied to the face (a) and the face pressure Pb (MPa) applied to the face (B, b) preferably satisfy 0.2 XPA Pb < 2 XPA. When a plurality of faces (B, b) are present, it is preferable that all the faces (B, b) satisfy the condition of 0.2 XPa Pb 2 XPa. The surface (B, b) is preferable because it prevents the press molding machine from continuously applying excessive pressure to the molding base material, and can prevent the molding base material from moving (shifting) in the cavity of the molding die and the surface of the press molded product from generating appearance defects such as wrinkles during press molding. For the same reason, it is more preferably in the range of 0.5 XPA.ltoreq.Pb.ltoreq.Pa. The range may be obtained by combining any of the above upper limits with any of the above lower limits.

The appropriate surface pressure conditions for the surface pressures Pa (pressure holding) and Pb (pressure holding) in the pressure holding step are within the range of 0.1 to 5 MPa. Further, it is preferable that Pa (shaped) and Pb (shaped) in the shaping step are in the range of 0.5 to 10%.

From the viewpoint of reducing the dimensional change to a desired shape after the molded article is taken out from the molding die, the duration (dwell time) in the dwell step (IV) is preferably a time until the shaped sheet-like molding base material is solidified. Usually, it is about several minutes to 10 minutes. The thicker the thickness of the molded product is, and the higher the surface temperature of the molding die is, the longer the dwell time is. Therefore, from the viewpoint of improving the economy by shortening the pressure holding step (IV), it is preferably 600 seconds or less, and particularly preferably 300 seconds or less. In some cases, 60 seconds or more is preferable. As a method for shortening the pressure holding step (IV), it is preferable to use a method in which the surface temperature of the molding die is set to a temperature sufficiently lower than the solid-state temperature of the resin, and the molding die is heated at a high speed and cooled at a high speed

In the present invention, the method of press-molding the sheet-like molding base material containing at least the reinforcing fibers and the matrix resin can be selected according to the shape of the desired molded article. Here, the press molding is a method of obtaining a molded product by applying deformation such as bending, shearing, and compression to various materials typified by metals, plastic materials, and ceramic materials using a processing machine, a mold, a tool, or the like. Examples of the molding method include drawing, deep drawing, flanging, corrugating (corrugating), crimping, and press molding. Examples of the method of press molding include a die press molding method in which molding is performed using a die, a rubber press molding method (hydrostatic press molding method), and an extrusion molding method. In the above press molding method, from the viewpoint of the degree of freedom of molding pressure and temperature, it is preferable to use: a die press molding method in which molding is performed using a metal die.

In the above-described press molding method, a hot press method and a cold press method can be used for the molding base material including at least the reinforcing fibers and the thermoplastic resin, but the press molding method of the present invention is not particularly limited, and a cold press method excellent in economy and workability is preferably used, and the hot press method is: a method of producing a molded article, which comprises disposing a molding base material in a mold in advance, pressing and heating the molding base material while closing the mold, and then cooling the molding material by cooling the mold while closing the mold; the cold pressing method comprises the following steps: a method of heating the molding material to a temperature equal to or higher than the melting temperature of the thermoplastic resin in advance by a heating device exemplified by a far infrared heater, a hot plate, a high temperature furnace, induction heating, or the like, placing the molding material on a mold to be the lower surface of the molding die in a state where the thermoplastic resin is melted and softened, closing the mold, and then performing pressure cooling.

In addition, in the step (V), the surface temperature of the cavity of the molding die is preferably lowered, and in this case, when the resin in the sheet-like molding base material is a thermoplastic resin, the surface temperature of the cavity of the molding die is lowered to a softening point or lower, and when the resin in the sheet-like molding base material is a thermosetting resin, the surface temperature of the cavity of the molding die is lowered to a glass transition temperature or lower, so that the molded article can be taken out from the molding die in a state in which the dimension of the molded article is stabilized.

When a thermosetting resin is used as the sheet-shaped molding base material, it is preferable to apply sufficient heat for melting or softening the thermosetting resin before forming the crosslinked structure and curing, and then set the heat to a glass transition temperature or lower, so that the risk of dimensional change of the molded article to be press-molded is minimized. The glass transition temperature can be determined by dsc (differential Scanning calorimetry). The temperature of the glass transition temperature can be determined by measuring the temperature at the temperature increase rate of 10 ℃/min and the temperature at the intersection of the extension lines of the base line of the endothermic portion and the rise start line of the measured DSC curve in the obtained DSC curve.

[ sheet-like molded base Material ]

In the present invention, the sheet-like molding base material contains at least a resin and a reinforcing fiber, and the resin is preferably selected from thermoplastic resins and thermosetting resins from the viewpoints of the formability of a molded article, the selectivity of surface appearance, mechanical properties, and the improvement of lightweight properties.

Examples of the reinforcing fibers constituting the sheet-like molding base material used in the method for producing a press-molded article of the present invention include: metal fibers such as aluminum and stainless steel; insulating fibers such as PAN-based, rayon-based, lignin-based, pitch-based carbon fibers, graphite fibers, and glass; organic fibers such as aramid, PBO, polyphenylene sulfide, and the like; and inorganic fibers such as silicon carbide and silicon nitride. Further, these fibers may be surface-treated. As the surface treatment, in addition to the deposition treatment of the metal as the conductor, there are treatment with a coupling agent, treatment with a sizing agent, treatment with a binder, adhesion treatment of an additive, and the like. These fibers may be used alone in 1 kind, or may be used in combination in 2 or more kinds. Among them, PAN-based, pitch-based, rayon-based, and other carbon fibers having excellent specific strength and specific rigidity are preferably used from the viewpoint of the effect of weight reduction. In addition, from the viewpoint of improving the economy of the molded article obtained, glass fibers are preferably used, and from the viewpoint of balance between mechanical properties and economy, carbon fibers and glass fibers are particularly preferably used in combination. Further, in view of enhancing the shape-imparting property of the molded product, it is preferable to use aramid fibers, and carbon fibers and aramid fibers are preferably used in combination within a range not to impair the effect of the present invention. In addition, from the viewpoint of enhancing the electrical conductivity of the molded product, a reinforcing fiber coated with a metal such as nickel or copper may be used. Among these, PAN-based carbon fibers having excellent mechanical properties such as strength and elastic modulus can be more preferably used.

The reinforcing fibers are substantially monofilament-like fibers, and are preferably carbon fibers randomly dispersed in the sheet-like molding material. By using the reinforcing fibers in this form, the reinforcing fibers can be easily formed into a complicated shape when a sheet-like molding base material is press-molded. In addition, in this form, the reinforcing fibers are preferably formed to make the voids formed by the reinforcing fibers dense, and the weak portions at the fiber bundle ends of the reinforcing fibers in the sheet-like molding base material can be minimized, so that a press-molded product having isotropy in addition to excellent reinforcing efficiency and reliability can be obtained.

Here, the substantially monofilament-like shape means that a fine fineness strand having less than 500 reinforcing fiber strands is present. Further preferably in the form of monofilaments, i.e. in the form of a single yarn.

Here, the substantially monofilament-like shape or the dispersion of the reinforcing fibers into the monofilament-like shape means that the ratio of the single fibers having a two-dimensional orientation angle of 1 degree or more (hereinafter also referred to as a fiber dispersion ratio) to the reinforcing fibers arbitrarily selected from the sheet-like molding base material is 80% or more. In other words, it means that: the sheet-like molding base material has less than 20% of bundles formed by contacting and arranging 2 or more filaments in parallel. Therefore, it is particularly preferable that the mass fraction of the fiber bundle in which the number of filaments in at least the reinforcing fiber is 100 or less corresponds to 100%.

Also, the reinforcing fibers are more preferably randomly dispersed. Here, the reinforcing fibers are randomly dispersed, and means that the arithmetic average of the two-dimensional orientation angles of arbitrarily selected single fibers in the sheet-like molding base material is in the range of 30 degrees or more and 60 degrees or less. The two-dimensional orientation angle is an angle formed by a single fiber of the reinforcing fiber and a single fiber intersecting the single fiber, and is defined as an angle on an acute angle side of 0 degree to 90 degrees in an angle formed by the intersecting single fibers.

The two-dimensional orientation angle is further explained using the drawings. Fig. 5 (a) is a schematic view of a two-dimensional projection, and fig. 5 (b) is a schematic view of a cross-sectional direction. In fig. 5 (a), when the single fiber 13a is used as a reference, the single fiber 13a intersects with the other single fibers 13b to 13 f. Here, the crossing means a state where a single fiber serving as a reference is observed to cross another single fiber in a two-dimensional plane to be observed, and the single fiber 13a and the single fibers 13b to 13f do not necessarily have to be in contact with each other. In the detailed description using the drawings, fig. 5 (b) is a cross-sectional view taken perpendicular to the longitudinal direction of the single fiber 13a, and the single fiber 13a extends toward the back side of the paper. The

single fibers

13a, 13e, and 13f do not contact each other. However, when two-dimensional projection is performed as shown in fig. 5 (a), the single fiber 13a and the single fibers 13b to 13f intersect with each other, and a two-dimensional orientation angle is present. That is, the intersection includes a state in which intersection is observed in the case of projection observation. That is, when the single fiber 13a as a reference is observed, all the single fibers 13b to 13f are the evaluation target of the two-dimensional orientation angle, and in fig. 5 (a), the two-dimensional orientation angle is an angle on the acute angle side in the range of 0 degree or more and 90 degrees or less among 2 angles formed by 2 single fibers intersecting (the two-dimensional orientation angle 14 is shown in fig. 5).

The method for measuring the two-dimensional orientation angle is not particularly limited, and for example, a method of observing the orientation of the reinforcing fibers from the surface of a sheet-like molding base material or a press-molded article can be exemplified. The average value of the two-dimensional orientation angle was measured in the following manner. That is, the average value of the two-dimensional orientation angles of the randomly selected single fibers (the single fibers 13a in fig. 5) and all the single fibers (the single fibers 13b to 13f in fig. 5) intersecting therewith was measured. For example, when there are a plurality of other single fibers intersecting with a certain single fiber, an arithmetic average value obtained by randomly selecting 20 other intersecting single fibers may be used instead. The measurement was repeated 5 times in total with respect to the other single fibers, and the arithmetic average thereof was calculated as the arithmetic average of the two-dimensional orientation angle.

By making the reinforcing fibers substantially monofilament-like and randomly dispersed, the performance imparted by the reinforcing fibers dispersed substantially monofilament-like can be improved to the maximum. Moreover, isotropic mechanical properties can be imparted to a sheet-like molding base material and a press-molded article. From this viewpoint, the fiber dispersion rate of the reinforcing fibers is preferably 80% or more, and is more preferably as close to 100%. The arithmetic average of the two-dimensional orientation angles of the reinforcing fibers is preferably in the range of 40 degrees or more and 50 degrees or less, and is more preferably closer to 45 degrees, which is an ideal angle. The preferred range of the two-dimensional orientation angle may have any of the above upper limits as an upper limit, and any of the above lower limits as a lower limit.

From the viewpoint of enhancing the reinforcing effect of the reinforcing fibers in the sheet-like molding base material and satisfying the lightweight property, the blending ratio of the reinforcing fibers in the sheet-like molding base material is preferably within a range of 10 to 50 vol%. The volume content of the reinforcing fibers is preferably 50 vol% or less because the reinforcing effect from the reinforcing fibers can be made sufficient. On the other hand, when the volume content of the reinforcing fibers is 10 vol% or more, the volume content of the reinforcing fibers with respect to the resin is relatively large, the reinforcing fibers in the sheet-like molding base material are bonded to each other, the reinforcing effect of the reinforcing fibers can be made sufficient, and a resin film is easily formed on the surface of the press-molded product, and therefore, the mechanical properties and the surface appearance of the press-molded product can be satisfied, which is preferable. If the blending ratio of the reinforcing fibers is more than 50 vol%, although a reinforcing effect can be obtained, the resin film is not easily formed. If the blending ratio of the reinforcing fiber is less than 10 vol%, it is difficult to obtain a reinforcing effect.

Examples of the resin constituting the sheet-like molding base material used in the method for producing a press-molded article of the present invention include thermoplastic resins and thermosetting resins. In the present invention, a thermosetting resin and a thermoplastic resin may be mixed, and in this case, a component occupying an amount of more than 50 mass% among components constituting the resin is referred to as the name of the resin.

The resin in the present invention can contain at least 1 or more thermoplastic resins. Examples of the thermoplastic resin include thermoplastic resins selected from the group consisting of: polyarylene sulfides such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and liquid crystal polyesters, polyolefins such as Polyethylene (PE), polypropylene (PP), and polybutylene, Polyoxymethylene (POM), Polyamide (PA), and Polyphenylene Sulfide (PPs); crystalline resins such as fluorine-based resins (e.g., Polyketone (PK), Polyetherketone (PEK), Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), Polyethernitrile (PEN), and polytetrafluoroethylene), and Liquid Crystal Polymers (LCP) "; non-crystalline resins such as Polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), Polyimide (PI), polyamide imide (PAI), polyether imide (PEI), Polysulfone (PSU), polyether sulfone, and Polyarylate (PAR) "in addition to styrene resins, thermoplastic elastomers such as phenol resins, phenoxy resins, and polystyrene, polyolefin resins, polyurethane resins, polyester resins, polyamide resins, polybutadiene resins, polyisoprene resins, fluorine resins, and acrylonitrile resins, copolymers and modifications thereof, and the like. Among them, from the viewpoint of lightweight of the obtained molded article, polyolefin is preferable, from the viewpoint of strength, polyamide is preferable, from the viewpoint of surface appearance, amorphous resin such as polycarbonate and styrene resin is preferable, polyarylene sulfide is preferable from the viewpoint of heat resistance, polyether ether ketone is preferable from the viewpoint of continuous use temperature, and further, from the viewpoint of chemical resistance, fluorine-based resin is preferably used.

The resin in the present invention can contain at least 1 or more thermosetting resins. Examples of the thermosetting resin include at least 2 kinds of resins selected from unsaturated polyesters, vinyl esters, epoxy resins, phenol resins, urea resins, melamine resins, thermosetting polyimides, copolymers and modifications thereof, and mixtures thereof. From the viewpoint of mechanical properties of the obtained molded article, an epoxy resin can be preferably used. In addition, from the viewpoint of surface appearance design, unsaturated polyester, vinyl ester, and epoxy resin can be preferably used. From the viewpoint of flame retardancy, a phenol resin can be preferably used.

The resin may contain an impact resistance improver such as an elastomer or a rubber component, other fillers, and additives within a range not to impair the object of the present invention. Examples of the filler and the additive include an inorganic filler, a flame retardant, a conductivity-imparting agent, a crystal nucleating agent, an ultraviolet absorber, an antioxidant, a vibration-damping agent, a coloring-preventing agent, a heat stabilizer, a mold release agent, an antistatic agent, a plasticizer, a lubricant, a coloring agent, a foaming agent, and a coupling agent.

The binder component may be contained from various viewpoints such as packing of the reinforcing fiber mat, improvement of the impregnation property between the reinforcing fiber mat and the resin, and improvement of the mechanical properties of the sheet-shaped molding base material including the reinforcing fiber mat and the resin. The binder component may be any of a thermoplastic resin, a thermosetting resin, and a mixture or copolymer thereof, as long as the mechanical properties of a press-molded article using the sheet-like molding base material of the present invention are not impaired and the steps of the production method are not impaired.

In addition, from the viewpoint of shape-forming properties and ease of production of the sheet-like molding base material, the resin and binder component constituting the sheet-like molding base material in the present invention are preferably thermoplastic resins. The form of the thermoplastic resin can be appropriately selected from the forms of a sheet, a film, a nonwoven fabric, a fiber, a particle, and a liquid. The form of the sheet-shaped molding base material of the present invention is not particularly limited insofar as it does not inhibit the mechanical properties of the press-molded article using the sheet-shaped molding base material and the steps in the production method thereof, but the sheet or the film is preferably selected from the viewpoints of workability, productivity, and economy in the impregnation step with the reinforcing fiber mat described above, and the form of the nonwoven fabric or the fiber is preferably selected from the viewpoints of impregnation with the reinforcing fiber mat, and the form of the fiber or the particle is preferably selected from the viewpoints of easy mixing of the resin with the reinforcing fiber mat. The thickness of the film or sheet may be any thickness that can satisfy the content of the resin in the sheet-like molding base material. The fiber diameter of the nonwoven fabric or the fiber may be generally commercially available, and when the reinforcing fiber and the resin fiber are mixed to form a mixed mat, it is preferable to select a fiber diameter equal to or larger than the diameter of the reinforcing fiber in view of stability of the process. In the case of the particles, the particle size is not particularly limited, but in the case of mixing with a reinforcing fiber mat to form a mixed mat, it is preferable to appropriately adjust the particle size from the viewpoint of preventing the particles from falling off in the step. A thermosetting resin can be preferably used from the viewpoint of stability of mechanical properties, reliability, and shaping properties. The shape may be applied directly to the reinforcing fiber mat in a liquid state to impregnate the reinforcing fiber mat, or may be once formed into a film shape and then laminated with the reinforcing fiber mat to impregnate the reinforcing fiber mat.

The reinforcing fibers in the present invention are preferably in the form of a nonwoven fabric from the viewpoint of ease of impregnation of the reinforcing fibers with the resin. By providing the reinforcing fibers in the form of a nonwoven fabric, the fibers can be easily impregnated with a thermoplastic resin having a generally high viscosity, in addition to the ease of handling of the nonwoven fabric itself, and therefore, it is preferable. The nonwoven fabric-like form herein refers to a form in which strands and/or monofilaments of reinforcing fibers are randomly dispersed in a planar form, and examples thereof include forms such as chopped strand mats, continuous strand mats, papermaking mats, carding mats, and air-laid mats (hereinafter, these are collectively referred to as reinforcing fiber mats).

Examples of the reinforcing fibers that do not take the above-described form include sheet substrates, woven fabric substrates, and non-crimped (non-crimp) substrates in which reinforcing fibers are arranged in a single direction. In these forms, since the reinforcing fibers are regularly and densely arranged, voids in the sheet-shaped molding base material are reduced, impregnation with resin is extremely difficult, and there are cases where an unimpregnated portion is formed or options of impregnation means and resin types are greatly limited.

As a method for producing a reinforcing fiber mat, for example, a method for producing a reinforcing fiber mat by dispersing reinforcing fibers in advance into a bundle and/or a substantially monofilament form is known. As a method for producing the reinforcing fiber mat, a dry process such as an air-laid method in which reinforcing fibers are dispersed into a sheet by an air stream, a carding method in which reinforcing fibers are formed into a sheet by finishing the shape while mechanically carding, and a wet process using a Radright method (japanese: ラドライト method) in which reinforcing fibers are stirred in water to form a sheet are known. As a method of making the reinforcing fibers closer to a monofilament shape, in the dry process, a method of providing a spreader bar, a method of further vibrating the spreader bar, a method of further refining the mesh of a carding machine, a method of adjusting the rotational speed of the carding machine, and the like can be exemplified. In the wet process, a method of adjusting the stirring condition of the reinforcing fibers, a method of thinning the reinforcing fiber concentration of the dispersion, a method of adjusting the viscosity of the dispersion, a method of suppressing the eddy current when the dispersion is transferred, and the like can be exemplified. It is particularly preferable that the reinforcing fiber mat is manufactured by a wet process, and the proportion of the reinforcing fibers in the reinforcing fiber mat can be easily adjusted by increasing the concentration of the fibers to be fed, adjusting the flow rate of the dispersion, and adjusting the speed of the mesh conveyor. For example, it is preferable to reduce the speed of the mesh conveyor relative to the flow speed of the dispersion liquid, because the orientation of the fibers in the obtained reinforcing fiber mat is not easily oriented in the drawing direction, and a bulky reinforcing fiber mat can be produced. The reinforcing fiber mat may be composed of the reinforcing fibers alone, or may be composed of the reinforcing fibers mixed with a matrix resin component in a powder or fiber form. In addition, the reinforcing fibers may be mixed with an organic compound or an inorganic compound.

Further, the reinforcing fiber mat may be impregnated with a resin in advance. In view of ease of production, it is preferable to use a method in which a reinforcing fiber mat is impregnated with a resin by applying a pressure to the reinforcing fiber mat while the resin is heated to a temperature equal to or higher than the melting or softening temperature. Specifically, a method of melt-impregnating a laminate in which resins are arranged from both sides in the thickness direction of the reinforcing fiber mat can be preferably exemplified.

As the apparatus for carrying out each of the above methods, a compression molding machine and a double belt press can be suitably used. In the former case, the productivity can be improved by providing a batch type pressurizing system in which 2 or more heating and cooling units are arranged in parallel. In the latter case, continuous processing can be easily performed, and therefore, the continuous productivity is excellent.

When the sheet-like molding base material is a base material having an expansion ratio of 150 to 1000% in the thickness direction when heated to the melting temperature or softening temperature of the resin constituting the base material, the heated sheet-like molding base material is easily shaped when it is put into a cavity of a molding die and compression molding is performed, and the shape of a compression-molded product is easily obtained, so that it is preferable. By expanding the sheet-like molding base material shaped in the molding die cavity in the thickness direction of the molding die cavity, molding can be performed at a low press molding pressure by the pressure due to the expansion force of the sheet-like molding base material even if the pressure applied from the press molding machine is reduced. From the viewpoint of workability, the expansion ratio is preferably in the range of 200 to 800% in the thickness direction. In addition, from the viewpoint of utilizing the expansion force and improving the surface appearance of the molded product, the thickness direction is preferably in the range of 300 to 600%. The range may be obtained by combining any of the above upper limits with any of the above lower limits.

Here, the expansion ratio (t3) is an index indicating the degree of expansion of the sheet-like molding base material in a softened state, and is expressed by the following formula using the thicknesses (t1) and (t2) of the molding base material, where (t1) is the thickness of the sheet-like molding base material at a temperature of 23 ℃, and (t2) is the thickness of the sheet-like molding base material at a temperature 40 ℃ higher than the melting point of the thermoplastic resin when the resin contained in the sheet-like molding base material is a thermoplastic resin, and the thickness of the sheet-like molding base material at a temperature at which the thermosetting resin has the lowest viscosity when the resin contained in the sheet-like molding base material is a thermosetting resin.

·t3＝t2/t1×100(％)

In the measurement of the thicknesses t1 and t2 of the molded base materials, the measurement samples were exemplified as 100mm long and 100mm wide. the measurement points at t1 and t2 are the same location in the measurement sample, and thus the expansion ratio can be measured with high accuracy. The measurement point is set to 5 points or more, and when the measurement site is, for example, a 5-point measurement, the measurement point may be exemplified by a position at which the center of the measurement sample and the center portion are moved up, down, left, and right by 40 mm.

In addition, the reinforcing fibers in the sheet-like molding base material preferably have a mass-average fiber length of 1 to 15mm from the viewpoint of enhancing the reinforcing efficiency of the reinforcing fibers to the press-molded article and achieving the expansion ratio. By setting the mass-average fiber length of the reinforcing fibers to 1mm or more, the probability that the reinforcing fibers are present in the thickness direction in the sheet-like molding base material becomes high, and therefore, the sheet-like molding base material with small thickness variation at the time of swelling can be produced. Further, the quality of the reinforcing fiber mat can be improved, and therefore the surface appearance of the press-molded article is improved. On the other hand, when the mass-average fiber length of the reinforcing fibers is 15mm or less, the reinforcing fibers are less likely to bend by their own weight in the sheet-like molding base material, and the development of mechanical properties is not hindered, so that the reinforcing fibers are preferable. If the mass-average fiber length is less than 1mm, aggregation is liable to occur, resulting in a decrease in dispersibility. If the mass average fiber length is more than 15mm, the reinforcing fiber is easily bent by its own weight, and the mechanical properties are deteriorated. The mass-average fiber length of the reinforcing fiber can be calculated as follows: the resin component of the sheet-like molding base material is removed by a method such as burning and elution, 400 is randomly selected from the remaining reinforcing fibers, and the length thereof is measured to 10 μm units, and the mass-average fiber length thereof is calculated.

The press-molded article obtained by the method for producing a press-molded article of the present invention includes, for example: electric and electronic equipment parts such as "housings, trays, chassis, interior parts, and housings of home electric appliances such as personal computers, displays, OA equipment", and the like, "various components," various frames, various hinges, various arms, various axles, various wheel bearings, various beams, "cowl, roof, door, fender, trunk lid, side panel, back panel, front body, underbody, various pillars, various components, various frames, various beams, various brackets, various rails, exterior panels such as various hinges, or body parts," "bumper, bumper beam, trim, undercover, engine hood, cowling, spoiler, cowl vent, exterior parts such as streamline parts," "instrument panel, seat frame, door trim, pillar trim, steering wheel, various modules, and the like" structural parts for automobiles and motorcycles, interior parts such as "housings, trays, chassis, interior parts such as" home electric and electronic equipment parts such as "personal computers, displays, OA equipment," and the like, Parts for automobiles, motorcycles, and the like such as "battery tray, headlamp bracket, pedal housing, protector, lamp reflector, lamp housing, soundproof cover, spare wheel cover", and parts for aircraft such as "landing gear pod", wingtip winglet, spoiler, leading edge, gangway, elevator, cowling, wing rib, and seat ". From the viewpoint of mechanical properties, the resin composition is preferably used for interior and exterior materials for automobiles, housings for electric and electronic devices, structural materials for bicycles and sporting goods, interior materials for aircrafts, and cases for transportation. Among these, the method is particularly suitable for use in a module component composed of a plurality of components.

Examples

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples.

[ evaluation/measurement method ]

(1) Sheet-like molding base material and volume content of reinforcing fiber in press-molded article

A test piece 10mm long and 10mm wide was cut out from a sheet-like molding base material, the mass Ws and the volume Vs of the porous body (a) were measured, and then the test piece was heated in air at 500 ℃ for 30 minutes to burn out the resin component, and the mass Wf of the remaining reinforcing fibers was measured and calculated according to the following formula.

Vf (% by volume) of the reinforcing fiber (Wf/ρ f)/{ Wf/ρ f + (Ws-Wf)/ρ r } × Vs × 100

ρ f: density (g/cm) of reinforcing fibers³)

ρ r: density of resin (g/cm)³)

Vs: apparent volume (cm) of porous body (a)³)

(2) Dispersion state of reinforcing fibers in molded base material

The case where the following (2-1) and (2-2) are satisfied is considered that the dispersion state of the fibers is random.

(2-1) sheet-like Molding base Material and fiber Dispersion State in Press-molded article

The reinforcing fiber mat was taken out from the sheet-like shaped base material in the same manner as in (1) above. The surface of the obtained reinforcing fiber mat was observed with an electron microscope (VHX-500, manufactured by KEYENCE corporation), 1 single fiber was randomly selected, and the two-dimensional orientation angle of the single fiber and the other single fibers in contact therewith was measured. The magnification was 50 times. The two-dimensional orientation angle is an angle (acute angle side) of 0 to 90 degrees among 2 angles formed by 2 single fibers in contact with each other. The two-dimensional orientation angle was measured for 100 filaments selected from all the filaments in contact with the selected filaments. From the obtained results, the ratio of the number of single fibers having a two-dimensional orientation angle of 1 degree or more to the total number of all the single fibers having a measured two-dimensional orientation angle was obtained as a fiber dispersion ratio, and the fiber dispersion ratio of 90% or more was defined as the 1 st condition for determining random. When the reinforcing fibers were observed to be bundled during observation, the fibers were bundled and it was determined that the fibers were not in an excellent dispersed state.

(2-2) sheet-shaped Molding base and two-dimensional orientation Angle of Press-molded article

The reinforcing fiber mat was taken out from the sheet-like shaped base material in the same manner as in (1) above. The obtained reinforcing fiber mat was observed with an electron microscope (VHX-500, manufactured by KEYENCE corporation), 1 single fiber was randomly selected, and the two-dimensional orientation angle of the single fiber and the other single fibers intersecting the single fiber was measured by image observation. The orientation angle is an angle (acute angle side) of 0 to 90 degrees among 2 angles formed by 2 crossing single fibers. The number of measurements of the two-dimensional orientation angle per 1 single fiber was set to be n ═ 20. A total of 5 single fibers were selected and subjected to the same measurement, and the average value thereof was defined as a two-dimensional orientation angle, and the case of 40 degrees to 50 degrees was defined as the 2 nd condition for judgment of randomness.

(3) Expansion ratio in thickness direction of molded base material

The expansion ratio after heating was measured by the following steps (a) to (C). All the thickness measurements were carried out with a vernier caliper (digital vernier caliper (CD-67S20PS (trade name)) manufactured by Mitutoyo corporation).

(A) The thickness of the molded substrate in the form of a sheet at room temperature (23 ℃) was measured (t 1).

(B) After the molded article is taken out from the heating apparatus (the temperature is higher than the melting point by 40 ℃ in the case where the resin is a thermoplastic resin, and the temperature is such that the thermosetting resin has the lowest viscosity at the time of heating and thermosetting in the case where the resin is a thermosetting resin), the thickness of the molded article after the molten and softened molded article is cooled in the air is measured (t 2). The measurement sample had a length of 100mm and a width of 100 mm. the measurement points at t1 and t2 are the same sites in the measurement sample. The measurement points were set to 5 points, and the center of the measurement sample and the positions of the center of the measurement sample moved up and down and left and right by 40mm were set as the measurement points.

(C) The expansion ratio of the heated molded substrate was calculated by the following equation (t 3). T3 was obtained from the 5-point measurement, and the average value was obtained.

t3[％]＝(t2[mm]/t1[mm])×100

(4) Measurement of pressure applied to surface (a) and surface (b) of a molding die in a shaping step and a pressure holding step

The measurement is performed by a pressure sensor disposed on the surface (a) and the surface (b) having an angle of the press mold. The pressure sensor is provided at an equally divided position (n is 5) on the surface (a) of the molded product. At the vertical wall portion (corresponding to the surface (b)), 1 pressure sensor is disposed in the longitudinal direction. There were a plurality of surfaces (b), and 1-position pressure sensor was attached to each surface (b) to measure the pressure on the plurality of surfaces (b). The arithmetic mean of the values measured by the pressure sensor is set as the surface pressures of the surface (a) and the surface (b). Then, the deviation of the pressure applied to each surface is obtained as follows: the standard deviation is calculated from each measured value, and the standard deviation is divided by the average value to calculate a coefficient of variation (CV value (%)) as an index of the deviation. The deviation is calculated by dividing the plane (a) and the plane (b). When both the surface (a) and the surface (B) satisfy the strip of the surface (B), the value of the surface (B) is shown as the value of the surface (B) which is one of the surface (a) having a large inclination and a low surface pressure. In the shaping step and the pressure holding step, if the molding base material is brought into contact with the molding die, the pressure applied to the molding base material is equal to the pressure applied to the corresponding surface (a) and surface (b) of the molding die.

(5) Pressure applied from press forming machine to projection surface of molded product

The output of the press molding machine read by a pressure monitor provided in the press molding machine is represented by Fp, and the Fp is divided by the projection area Sm of the molded product, whereby the pressure (σ p) applied to the projection surface of the molded product is calculated from the following equation.

σp[MPa]＝Fp[kN]/Sm[mm²]×1000

(6) Evaluation of appearance of molded article

Regarding the molded article obtained by press molding, molding defects such as scratches and wrinkles were visually observed in the flat portion (surface (a) portion) and the standing wall portion (surface (B) portion), respectively. As for the evaluation index, a molded article having no scratch or wrinkle was regarded as "good" indicating pass, and a molded article having scratch or wrinkle was regarded as "bad" indicating fail.

< Molding die used >

[ Molding die M-1]

As the molding die M-1, a metal box-shaped die formed of upper and lower dies is used. The top and bottom surfaces have four sides (the same applies to M-2 to M-4 hereinafter).

The projection surface of the molded article of the upper mold (convex portion) had dimensions of 196mm in length, 196mm in width and 22mm in height.

The projection surface of the molded article of the lower mold (concave part) had a length of 200mm, a width of 200mm and a height of 20 mm.

The angle between the surface (a) and the pressing plate is 0 degree

The angle between the surface (b) and the pressing plate is 90 degrees

In addition, the pressure sensors are provided in 5 locations in total, i.e., 1 point in the center of the lower die and the positions (4 locations) in which the corners extending from the center point of the upper die to the four sides are 100mm in the plane (a), and the pressure sensors are provided in 1 location (4 locations) in the center of each side in the plane (b).

[ Molding die M-2]

As the molding die M-2, a metal box-shaped die formed of upper and lower dies is used.

The dimensions of the convex portion of the upper mold, the dimensions of the concave portion of the lower mold, the angle between the surface (a) and the platen, and the position of the pressure sensor are the same as those of M-1.

Angle of surface (b) to platen: 45 degree

[ Molding die M-3]

As the molding die M-3, a metal box-shaped die formed of upper and lower dies is used.

The dimensions of the convex portion as the upper mold, the dimensions of the concave portion as the lower mold, and the position of the pressure sensor are the same as those of M-1.

Angle of surface (a) to platen: 45 degree

Angle of surface (b) to platen: 60 degree

[ Forming mold M-4]

As the molding die M-4, a metal box-shaped die formed of upper and lower dies was used.

Angle of surface (a) to platen: 15 degree

Angle of surface (b) to platen: 70 degree

< materials used >

[ carbon fibers ]

A continuous carbon fiber having a total number of filaments of 12,000 is obtained by spinning, firing and surface oxidation of a copolymer mainly composed of polyacrylonitrile. The properties of the continuous carbon fiber are as follows.

Specific gravity: 1.8

Tensile strength: 4600MPa

Tensile modulus of elasticity: 220GPa

Tensile elongation at break: 2.1 percent of

[ PP resin ]

A resin sheet was prepared which contained 80 mass% of an unmodified polypropylene resin ("Prime Polypropylene" (registered trademark) J105G, manufactured by Prime Polymer Co., Ltd.) and 20 mass% of an acid-modified polypropylene resin ("ADMER" (registered trademark) QB510, manufactured by Mitsui chemical Co., Ltd.), and had a weight per unit area of 200g/m²。

[ PPS resin ]

A polyphenylene sulfide resin ("Torrelina" (registered trademark) A900, manufactured by Toray corporation) was prepared in an amount of 268g/m in weight per unit area²The resin sheet of (1).

[ Molding base material S-1]

Carbon fibers were used as reinforcing fibers, which were cut into 5mm with a cylindrical cutter (cartridge cutter) to obtain chopped carbon fibers. A dispersion liquid containing water and a surfactant (polyoxyethylene lauryl ether (trade name) manufactured by Nacalai Tesque) at a concentration of 0.1 mass% was prepared, and a reinforcing fiber mat was prepared using this dispersion liquid and chopped carbon fibers. The manufacturing device comprises a dispersion tank and a linear conveying part (with an inclination angle of 30 degrees) connecting the dispersion tank and a paper making tank,the dispersion tank was a cylindrical vessel having an opening cock at the lower part thereof and a diameter of 1000 mm. An agitator is attached to an opening portion on the upper surface of the dispersion tank, and the chopped carbon fibers and the dispersion liquid (dispersion medium) can be fed through the opening portion. The paper-making tank is provided with a mesh conveyor having a paper-making surface with a width of 500mm at the bottom, and a conveyor capable of conveying a felt made of carbon fibers is connected to the mesh conveyor. The paper was made with the concentration of carbon fibers in the dispersion being 0.05 mass%. And drying the manufactured carbon fiber felt in a drying furnace at 200 ℃ for 30 minutes to obtain the reinforced fiber felt. The weight per unit area of the obtained felt was 90g/m²。

Next, a laminate was produced in which the reinforcing fiber mat and the PP resin were arranged in the order of [ PP resin/reinforcing fiber mat/PP resin ]. S-1 is obtained by further performing the following steps (i) to (iv). The characteristics are shown in table 1.

(i) The laminate was placed in a cavity of a press molding die preheated to 200 ℃, and the upper die and the lower die were closed to form a flat plate-shaped molding die.

(ii) Subsequently, the pressure was applied at 3MPa for 120 seconds, and the pressure was further maintained for 60 seconds.

(iii) Next, the cavity temperature was cooled to 50 ℃ while maintaining the pressure.

(iv) And opening the forming mold and taking out the formed base material.

[ Molding base material S-2]

Carbon fibers were used as reinforcing fibers, which were cut into 8mm pieces with a cylindrical cutter to obtain chopped carbon fibers. The reinforcing fiber mat was produced by the method described for the molding base material S-1. The weight per unit area of the obtained felt was 90g/m²。

Next, a laminate was produced in which the reinforcing fiber mat and the PP resin were arranged in the order of [ PP resin/reinforcing fiber mat/PP resin ]. S-2 is obtained by further passing through the steps (i) to (iv) described in the molding base material S-1 in this order. The characteristics are shown in table 1.

[ Molding base material S-3]

A reinforcing fiber mat was obtained by the method described in the molding substrate S-1, except that carbon fibers were used as the reinforcing fibers and the reinforcing fibers were cut into 15mm pieces with a cylindrical cutter. The weight per unit area of the obtained felt was 90g/m²。

Subsequently, the molded substrate S-3 is produced by passing the molding substrate S-1 through the steps (i) to (iv) in this order.

[ Molding base Material S-4]

A reinforcing fiber mat was obtained by the method described for the molded substrate S-1, except that carbon fibers were used as the reinforcing fibers and the reinforcing fibers were cut into 8mm pieces with a cylindrical cutter. The weight per unit area of the obtained felt was 90g/m²。

Next, a laminate was prepared by arranging the reinforcing fiber mat and the PPS resin in the order of [ PPS resin/reinforcing fiber mat/PPS resin ]. S-4 is obtained by further performing the following steps (i) to (iv). The characteristics are shown in table 1.

(i) The laminate was placed in a cavity of a press molding mold preheated to 320 ℃ and the molding mold was closed.

Steps (ii) to (iv) are the same as those of S-1.

[ Molding base material S-5]

Carbon fibers were used as reinforcing fibers, which were cut into 5mm pieces with a cylindrical cutter to obtain chopped carbon fibers. The chopped carbon fibers were fed into a cotton opener to obtain a cotton-like carbon fiber aggregate in which a large number of carbon fiber bundles having the first thickness were present. The reinforcing fiber assembly was fed into a carding machine having a cylindrical roll with a diameter of 600mm (the rotational speed of the cylindrical roll was 100rpm, and the speed of the doffer was 13 m/min), to form a reinforcing fiber mat made of carbon fibers. A large number of bundled carbon fibers are observed in the reinforcing fiber mat. The weight per unit area of the obtained felt was 90g/m²。

S-5 was obtained in the same manner as in S-1 except for the above-mentioned preparation method. The characteristics are shown in table 1.

[ Molding base material S-6]

According to the method described in the molded substrate S-1A reinforcing fiber mat is obtained. The weight per unit area of the obtained felt was 90g/m²。

Next, a laminate was produced in which the reinforcing fiber mat and the PP resin were arranged in the order of [ PP resin/reinforcing fiber mat/PP resin ]. S-6 is obtained by further passing through the steps (i) to (iv) described in the molding base material S-1 in this order. The properties are shown in table 1.

(example 1)

A molded article was molded by successively carrying out the following steps (I) to (V) using S-1 as a molding material and M-1 as a molding die. A hydraulic press molding machine was used for the press molding, and a far infrared heater was used for melting the molding base material. The molding base material was adjusted to have a size of 150% of the projection surface of the cavity of the molding die. The properties of the molded article are shown in Table 2.

A step (I): the molded substrate was heated to 200 ℃ to melt the thermoplastic resin.

Step (II): the temperature of the molding cavity was adjusted to 100 ℃ in advance, and 4 layers of the molten molding base material were stacked and immediately placed in the molding cavity.

Step (III): the molding die was closed, and a surface (a) orthogonal to the direction of pressure applied from the press molding machine was pressurized by the press molding machine so that the pressurizing force became 3MPa, and the shape was formed.

Step (IV): the applied pressure is released, and the thickness is fixed by position control to maintain the pressure. In this case, the surface pressure Pa of the surface (a) and the surface pressure Pb of the surface (b) indicated by the pressure sensor were 3MPa and 2.5MPa, respectively.

Step (V): after the step (IV) was maintained for 1 minute, the molding die was released and the molded article was released.

The obtained molded article was shaped into a shape corresponding to the cavity of the molding die, and had no wrinkles or scratches at any portion, and had a good surface state.

(example 2)

A press-molded article was obtained in the same manner as in example 1, except that S-2 was used as the molding material, M-2 was used as the molding die, the molding base material was adjusted in size so as to be 130% of the projection surface of the cavity of the molding die, and the pressing was performed by the press-molding machine so that the applied pressure was 15MPa with respect to the projection surface of the molding base material in step (III) and the molding was performed.

In the step (IV), the surface pressure Pa of the surface (a) and the surface pressure Pb of the surface (b) indicated by the pressure sensor are 3MPa and 3MPa, respectively.

The obtained molded article was shaped into a shape corresponding to the cavity of the molding die, and had no wrinkles or scratches at any portion, and had a good surface state. The properties of the molded article thus obtained are shown in Table 2.

(example 3)

The molding material S-3 and the molding die M-3 were used, and the following steps (I) to (V) were successively performed to mold a molded article. The same apparatus as in example 1 was used for press molding. The molding base material was adjusted to have a dimension of 110% of the projection plane of the cavity of the molding die. The properties of the molded article thus obtained are shown in Table 2.

The steps (I), (III) to (V) are the same as in example 1. In the step (II), the temperature of the cavity of the molding die was previously adjusted to 120 ℃, and the molten molding base materials were stacked in 2 layers and immediately placed in the cavity of the molding die.

The surface pressure Pa of the surface (a) and the surface pressure Pb of the surface (b) indicated by the pressure sensor were 3MPa and 2.5MPa, respectively.

(example 4)

The molding material S-4 and the molding die M-1 were used, and the following steps (I) to (V) were successively performed to mold a molded article. The same apparatus as in example 1 was used for press molding. The molding base material was adjusted to a size of 150% of the projection plane of the cavity of the molding die. The properties of the molded article thus obtained are shown in Table 2.

The steps (I), (IV) and (V) are the same as in example 1.

The same procedure as in example 1 was repeated, except that the temperature of the cavity of the molding die was adjusted to 80 ℃ in advance in step (II).

The same procedure as in example 1 was repeated except that in step (III), the pressing was performed so that the projection surface of the molding base material was pressurized to 10MPa by the pressing force from the press molding machine, and the molding was performed.

In the step (IV), the surface pressure Pa of the surface (a) displayed by the pressure sensor is 3MPa, and the surface pressure Pb of the surface (b) is 2.5 MPa.

The obtained molded article was shaped into a shape corresponding to the cavity of the molding die, and had no wrinkles or scratches at any portions, and had a good surface condition.

Comparative example 1

A molded article was molded by successively carrying out the following steps (I) to (V) using S-5 as a molding material and M-1 as a molding die. The same apparatus as in example 1 was used for press molding. The molding base material is adjusted so as to be 100% of the projection plane of the cavity of the molding die. The properties of the molded article thus obtained are shown in Table 2.

The steps (I), (III) and (V) are the same as in example 4.

The same procedure as in example 4 was repeated, except that the temperature of the cavity of the molding die was adjusted to 100 ℃ in the step (II).

In the step (IV), the surface pressure Pa of the surface (a) displayed by the pressure sensor is 0MPa, and the surface pressure Pb of the surface (b) is 0 MPa.

The obtained molded article was not shaped into a shape corresponding to the cavity of the molding die, and wrinkles and scratches were generated in the standing wall portion, and poor appearance was observed.

Comparative example 2

A press-molded article was obtained in the same manner as in comparative example 1, except that S-6 was used as the molding material, M-4 was used as the molding die, the molding base material was adjusted in size so as to be 80% of the projection surface of the cavity of the molding die, and the pressing force from the press-molding machine was applied to the projection surface of the molding base material and the molding was performed in step (III) so as to be 15 MPa. The properties of the molded article thus obtained are shown in Table 2.

Comparative example 3

A press-molded article was obtained in the same manner as in example 2, except that S-2 was used as the molding material, M-2 was used as the molding die, the molding base material was adjusted in size so as to be 130% of the projection surface of the cavity of the molding die, and the pressing force from the press-molding machine was applied to the projection surface of the molding base material in step (III) to form the molding base material while applying pressure so as to be 15 MPa. The properties of the molded article thus obtained are shown in Table 3.

[ Table 1]

[ Table 2]

[ TABLE 2]

[ Table 3]

[ TABLE 3]

[ study ]

In examples 1 to 4, even in the molded article having a standing wall and having a portion not receiving a pressure from the press molding apparatus, the molded article had no appearance defects such as wrinkles, and a beautiful molded article was obtained. According to the method, excessive pressurizing force is not required, so that a large-sized press molding device is not required to be introduced, and thus a press molded product can be obtained extremely economically without requiring a large cost. This is due to: the two-dimensional orientation angle of each surface of the obtained press-molded article is not different from the two-dimensional orientation angle of the sheet-like molding base material before press molding, and therefore the change in the surface state is small.

On the other hand, in comparative example 1, scratches were generated in the standing wall portions. This is believed to be due to: since the pressure applied in the shaping step is too low and the reinforcing fibers in the molding material are present in a bundle shape, the pressure generated by the molding material in the molding die is low, and the shape cannot be ensured. In comparative example 2, the inclination of the surface (B) of the molding die was gentle, the amount of reinforcing fibers in the molding material was small, and a flow phenomenon by pressurization occurred, thereby generating wrinkles in the standing wall portion of the molded article. Neither of comparative examples 1 and 2 was a press-molded article having an excellent surface appearance.

Industrial applicability

According to the present invention, it is possible to provide a method for producing a molded article having excellent shape-following properties and excellent appearance quality even in a shape in which a pressing force from a press molding machine is not sufficiently applied due to the shape of the molded article.

Description of the reference numerals

1 pressing board of pressing forming machine (Upper)

2 pressing plate of pressing forming machine (lower)

3 forming die convex part

4 concave part of forming die

6 die cavity of forming die after die assembly

7 direction of application of pressurizing force from press forming machine

8 Angle between horizontal plane of pressing plate and surface (a) of forming die

9 Angle of horizontal plane of pressing plate and surface (b) of forming die

10 Press molded article

11 surface (A) of the press molded article to be a reference

12 a surface (B) having a surface pressure in the range of 0 to 70% with respect to the reference surface (A)

13 a-13 f single fibers

14 two-dimensional orientation angle

15 side (a)

16 side (b)

17 spacer for controlling thickness

Claims

1. A method for producing a press-molded article, wherein a sheet-like molding base material, which is disposed in a cavity of a molding die and in which reinforcing fibers are randomly dispersed in a matrix resin, is press-molded by using a press-molding machine provided with the molding die,

the molding die comprises a molding die for a convex portion and a die for a concave portion for forming an opening portion of a molded article, the molding die for the convex portion corresponds to the concave portion, and a cavity is formed between the molding die for the concave portion and the molding die for the convex portion,

the molding die has at least one surface B, which is a surface A orthogonal to the direction of pressure applied to the molding die from the press-forming machine, the surface B being a surface where the applied pressure is in the range of 0 to 70% with respect to the surface A, assuming that the pressure applied to the surface A by the press-forming machine is 100%,

the manufacturing method comprises the following steps:

a shaping step III of applying a surface pressure of 1MPa or more to the surface A as an external pressure from the press molding machine; and

and a pressure maintaining step IV for maintaining a pressure applied from the press molding machine to the molding base material as an external pressure of 0.1MPa or less at a temperature lower than a resin solidification temperature without releasing the molding die after the shaping step III.

2. The method of producing a press-molded article according to claim 1, wherein in the shaping step III, the pressure applied from the press-molding machine to the molding base as an external pressure is 1MPa or more.

3. The method of manufacturing a press-molded article according to claim 1 or 2, wherein the molding die has:

a surface a having an inclination of 0 to 60 degrees with respect to the surface A; and

a surface b having an inclination of 45 to 90 degrees with respect to the surface A and having a larger inclination than the surface a,

at least 1 of the faces B corresponds to the face B.

4. The method of producing a press-molded article according to claim 1 or 2, wherein in the shaping step III, a surface pressure Pa applied to the surface a and a surface pressure Pb applied to the surface b satisfy 0.2 xPa.ltoreq.Pb.ltoreq.2xPa, where Pa and Pb are expressed in MPa.

5. The method of producing a press-molded article according to claim 1 or 2, wherein in the pressure maintaining step IV, a surface pressure Pa applied to the surface a and a surface pressure Pb applied to the surface b satisfy 0.2 XPa Pb 2 XPa, and the unit of Pa and Pb is MPa.

6. The method of producing a press-molded article according to claim 1 or 2, wherein in the shaping step III, a surface pressure applied to the sheet-like molding base material on the surface a in the cavity after the mold is clamped is within a range of ± 10% of a mean value of the pressures applied to the surface a,

the surface pressure applied to the sheet-like molding base material on the surface b in the cavity after the mold is clamped is within a range of ± 10% of the average value of the pressures applied to the surface b.

7. The method of producing a press-molded article according to claim 1 or 2, wherein a step II of disposing the sheet-like molding base material in a cavity of a molding die is provided before the shaping step III, and in the step II, the sheet-like molding base material is laminated with 2 or more layers.

8. The method of producing a press-molded article according to claim 1 or 2, wherein the holding pressure process IV is performed by position control of the press-molding machine.

9. The method of producing a press-molded article according to claim 1 or 2, wherein the step II is a step of disposing the melted molding base material in the molding die cavity, and the sheet-like molding base material is disposed so as to cover 90% or more of a projection surface of the molding die cavity in a direction orthogonal to a direction of the pressure applied from the press-molding machine.

10. The method of manufacturing a press-molded article according to claim 1 or 2, wherein the reinforcing fiber is substantially monofilament-like.

11. The method of manufacturing a press-molded article according to claim 1 or 2, wherein the reinforcing fiber is a carbon fiber.

12. The method of producing a press-molded article according to claim 1 or 2, wherein the matrix resin is selected from a thermoplastic resin and a thermosetting resin.

13. The method of producing a press-molded article according to claim 1 or 2, wherein a blending ratio of the reinforcing fiber blended in the molding base material is in a range of 10 to 50 vol%.

14. The method for producing a press-molded article according to claim 1 or 2, wherein the sheet-like molding base material has an expansion rate of 150 to 1000% in a thickness direction when heated to a melting temperature or a softening temperature of the base resin.

15. The method of producing a press-molded article according to claim 1 or 2, wherein the shaping step III is preceded by a preforming step of processing a sheet-like molding base material into an expanded shape of the molded article.

16. The method of producing a press-molded article according to claim 7, wherein in step II, the surface temperature of the cavity of the molding die is adjusted in advance to a temperature equal to or higher than the curing temperature or the solid-state temperature and equal to or lower than the decomposition temperature of the resin in the molding base material.

17. The method of producing a press-molded article according to claim 1 or 2, wherein the pressing step IV is followed by a step V of taking out the molded article from the molding die after lowering the surface temperature of the cavity of the molding die, and in the step V, the surface temperature of the cavity of the molding die is lowered to not more than the softening point of the thermoplastic resin when the resin in the sheet-like molding base is a thermoplastic resin, and the surface temperature of the cavity of the molding die is lowered to not more than the glass transition temperature of the thermosetting resin when the resin in the sheet-like molding base is a thermosetting resin.

18. A press-molded article produced by the method for producing a press-molded article according to claim 1, wherein the press-molded article is a molded article obtained by press-molding a sheet-like molding base material in which reinforcing fibers are randomly dispersed in a matrix resin, the molded article has a concave portion and has at least a surface a and a surface b forming the concave portion, and the two-dimensional orientation angle of the reinforcing fibers in the surface a and the surface b of the molded article is in the range of 30 degrees or more and 60 degrees or less,

surface a: the horizontal plane in the press-formed article,

face b: the inclined surface of the press-molded article forms an angle of 45 DEG to 90 DEG with the horizontal surface.

19. The press-molded article according to claim 18, wherein the two-dimensional orientation angle of the sheet-like molding base material before press molding is in a range of 30 degrees or more and 60 degrees or less.

20. The press-molded article according to claim 18 or 19, wherein the reinforcing fiber is a carbon fiber.

21. The press-formed article according to claim 18 or 19, wherein the reinforcing fiber is substantially monofilament-like.

22. The press-molded article according to claim 20, wherein the reinforcing fiber is substantially monofilament-like.

23. The press-molded article according to claim 18 or 19, wherein the matrix resin is selected from a thermoplastic resin or a thermosetting resin.